Choosing the right partner in life can help overcome its many pitfalls and challenges. But what if that partner could also influence your health in totally unexpected ways—what if their genes, and not only yours, are at play?
This, at least, seems to be the case in mice where the health of one mouse is influenced by the genetic makeup of cage mates, according to a new study. Scientists in the UK have found that many health traits, such as anxiety, body weight, immune defense and the rate at which the body heals from injury seem to be, in part, under the control of roommates’ genes. If the same is true in people, doctors one day might want to take into account not just the patient’s genome, but also that of their partner, before deciding on the right diagnosis and treatment.
We know that peer pressure can influence health—just think of smoking—but how genes in one individual affect the health of another is far less known. There’s evidence from animal studies that a mother’s genes influence the wellbeing of her babies, but the idea that social partners’ genes affect not just one’s behaviour but also the body, well that just seems far-fetched, doesn’t it?
It may sound like a crazy idea, but it is not. Animal breeders have seen this occur in livestock, dubbing it indirect or social genetic effects (SGE) to describe when genes of one individual impact the well-being of another. “Breeding more sociable animals is a way to increase welfare in pigs and chickens,” writes Piter Bijma in an e-mail. He’s a geneticist at the University of Wageningen in the Netherlands, who’s been studying SGE for a decade.
The study referenced above, published last month in PLOS Genetics by Oliver Stegle’s group at the European Bioinformatics Institute in Cambridge, UK, is the most comprehensive account of how SGE impact health. Amelie Baud, a postdoc in Stegle’s lab, and her colleagues measured how more than 100 health traits change in response to cage mates’ genetic makeup. By combining data from 2,500 mice, they were able to calculate how much of the variation in mouse health can be explained not just by their own genes, but also by the genes of their cage mates.
They found that partners’ genes influence about 12 per cent of the difference seen in anxiety levels and up to 18 per cent on the wound healing rate. Perhaps the most surprising was the finding that some aspects of the immune system are more impacted by the genes in other mice than in measured animals.
It’s hard to see at first how the immune system and wound healing could be orchestrated by someone else’s genes. But Stegle offered several explanations. The effect could be direct where an attentive cage mate might lick the wound and help it heal faster, whereas a scrappy one would only make it worse. Or, he said, the healing rate could be affected by stress, which is known to impede the immune system and healing process.
Although the role of SGE in humans is largely unknown, this could soon change. Bijma also writes: “I expect considerable research here in the coming years. One can easily imagine SGE in humans, e.g. in relation to obesity. For example, when behaviour of spouses is genetic—behaviour usually has a genetic component—and affects body weight, then there are SGE on obesity. This would not at all surprise me.”
It’s also easy to imagine how a stressful social life might take its toll on health, from relationships mired in addiction to a more innocuous scenario, as suggested by Baud, where the partners’ body clocks are out of sync. To an early riser, living with a night owl would not just be annoying—always short on sleep—but their health could be in peril.
An open question remains as to the nature of the genes in social partners that pull such mighty strings on those around them. But for now, Stegle says, it’s not necessary to tease apart how SGE work, as long as we recognize that they exist.
“Although SGE exist, their contribution is small and it’s more about understanding their influence,” he says. By doing so, doctors may help patients by recognizing and correcting damaging behaviour in their partners without even having to know which genes are involved. Their effect on the immune system could be especially strong for regenerative medicine where future therapies might involve tweaking the immune system to bolster the body’s ability to heal, or shutting it down to avoid graft rejection.
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